oa South African Journal of Chemistry - Speciation studies of some toxic metal complexes of glycylglycine in propylene glycol-water mixtures : research article

Volume 65, Issue 1
  • ISSN : 0379-4350



The formation equilibria of complexes of Pb(II), Cd(II) and Hg(II) with glycylglycine were investigated pH-metrically in propylene glycol-water mixtures (0-60 % v/v) at 303 K and an ionic strength of 0.16 mol L-1. The dominant species detected were ML+ and MLH2+ for Pb(II); MLH2+ and MLH+ for Cd(II) and ML+, ML and MLH+ are for Hg(II). The appropriateness of the experimental conditions was verified by introducing errors deliberately in the concentrations of ingredients and volume of the solution. The models containing different numbers of species were refined by using the computer program MINIQUAD75. Selection of the best fit chemical models was based on statistical parameters. The trend in variation of stability constants of the complexes with dielectric constant of the medium was attributed to electrostatic and non-electrostatic forces. Distribution diagrams and plausible equilibria for the formation and possible structures of the complex species are presented.

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